1. Field of the Invention
The present invention relates to an electricity generation control technology in a vehicle including an electricity generator and a continuously variable transmission.
2. Background Art
Recently, an electricity generation control system of which an electricity generation amount of an electricity generator which rotates following an output shaft of an engine is variable to efficiently perform an electricity generation has been developed. In general, the electricity generation control system increases an electricity generation amount during deceleration of the vehicle to recover the kinetic energy of the vehicle as a power. However, in a case where the power is insufficient while driving, the electricity generator is driven by an engine to generate electricity for the insufficient power.
There has been suggested a technology that does not permit the electricity generation by the engine in a case where an engine efficiency obtained from an engine drive torque and an engine rotation speed does not satisfy a necessary engine efficiency, while the vehicle is driving, and permits the electricity generation by the engine in a case where the engine efficiency is higher than the necessary engine efficiency, whereby it is possible to efficiently generate electricity    Patent Document 1: JP-A-2010-125877
In a device of the related art as disclosed in JP-A-2010-125877, while the vehicle is driving, in a case where the engine efficiency obtained from the engine drive torque and the engine rotation speed is excellent, the electricity generation by the engine drive while driving is permitted. However, it does not make any mention about a technology for changing the engine rotation speed for the purpose of improving the electricity generation efficiency at the time of generating electricity by the engine drive while driving.
Therefore, in the device of the related art disclosed in JP-A-2010-125877, when the electricity generation by the engine drive while driving is performed, it may be impossible to control the electricity generation so as to be performed in a state where the engine efficiency becomes best. In addition, since characteristics of an electricity generator are not considered, the electricity generation is frequently performed in a state where a relation between the fuel amount, which increases accompanied with the electricity generation, and the electricity generation amount is not best.
The above-described problems of the related art as disclosed in JP-A-2010-125877 will be described in detail by using maps illustrating an engine efficiency and an electricity generation efficiency as shown in FIGS. 16A and 16B. FIG. 16A in the lower side shows a map illustrating an engine efficiency with respect to an engine rotation speed and an engine drive torque. FIG. 16B in the upper side shows a map illustrating an electricity generation efficiency (defined as a value obtained by dividing the electricity generation amount by the fuel consumption amount) with respect to an engine rotation speed and an electricity generation drive torque.
In FIG. 16A, an engine efficiency in a case where the vehicle is driving in a normal state (constant load and constant speed) without performing the electricity generation is shown as state 1. Next, an engine efficiency in a case where an engine drive torque is added and thereby it approaches a state 2 in FIG. 16A is calculated. In a case where the engine efficiency obtained by the calculation is superior to threshold value of aimed engine efficiency, the electricity generation is permitted and a control point is transited to the state 2 to perform the electricity generation. However, in a case contrary to this, the electricity generation is not permitted. In addition, in FIG. 16A, a dotted curve illustrates an engine operation region, and the operation is not performed beyond the region. However, in the above-described control, since the engine rotation speed is not changed, it may be impossible to generate electricity in a point where the engine efficiency becomes best. In addition, in an electricity generation efficiency map shown in FIG. 16B, after it is transited from a state 1′ to a state 2′ and the electricity generation is performed in the state 2′, but the state 2′ is not a state where the electricity generation efficiency becomes best. Since the state where the engine efficiency becomes best and the state where the electricity generation efficiency becomes best are different from each other, it is preferable to consider the characteristics of the electricity generator for the best electricity generation efficiency.
As described above, in the device of the related art disclosed in JP-A-2010-125877, since a transmission gear ratio is not controlled at the time of generating electricity and the electricity generation state is determined by only the engine efficiency without considering the characteristics of the electricity generator, it may be impossible to generate electricity at a state where the electricity generation efficiency becomes best.